Question about listing token on uniswap or pancakeswap

Hi
I want to make an erc20 token so first I'm gathering information about the code in safemoon and liquidity on pancakeswap

Why does safemoon has a code of uniswap in the contract

But other tokens are listed on pancakeswap with liquidity and they didn't have the code of uniswap in the contract?

So what is the use of uniswap code in the contract of safemoon?